1. Technical Field
The invention relates generally to a system for controlling ignition in an internal combustion engine, and, more particularly, to an ignition coil having integrated ion sense capability with combustion and knock outputs.
2. Description of the Related Art
It is desirable to detect a misfire condition or a knock condition during the operation of an internal combustion engine. One approach taken in the art to detect misfire involves assessing the degree of engine speed (RPM) variation. Although such an approach does not require additional circuit components, it does require relatively extensive software to perform the evaluation, and, further, is incapable of producing accurate and reliable results over the entire engine speed and load range on a higher number of cylinder engines.
Another approach for determining misfire or knock involves the use of a so-called ion sense system. It is known that the combustion of an air/fuel mixture in an engine results in molecules in the cylinder being ionized. It is further known to apply a relatively high voltage across, for example, the electrodes of a spark plug just after the ignition operation to produce a current across the electrodes. Such current is known as ion current. The ion current that flows is proportional to the number of combustion ions present in the area of, for example, the spark plug gap referred to above, and is consequently indicative of the ionization throughout the entire cylinder as combustion occurs. The DC level or amount of ion current is indicative of the quantity of the combustion event, or whether in fact combustion has occurred at all (e.g., a misfire condition). An AC level of the ion current may also be used to determine whether knock exists. The ion sense approach is effective for any number of cylinder engines and various engine speed and load combinations.
A challenge for ion sense designers, however, arises from a characteristically short spark duration (e.g., 500-600 microseconds) compared to non-ion sense systems (e.g., 1000-1500 microseconds). This duration may become an issue at low engine speeds, which need a longer duration spark to initiate combustion, due to flow and charge mixture factors, among other things. One solution involves employing repetitive spark during a single combustion event (xe2x80x9cmultichargingxe2x80x9d) at low engine speeds. However, there are challenges with using multicharging. For example, one conventional approach applies repetitive spark over a fixed duration, which may in some instances interfere with knock detection (i.e., knock detection via analysis of ion current cannot be accomplished while sparking continues in the cylinder).
Another challenge involves determining the degree or quality of combustion. In another known system, the earliest time for beginning the processing of ion current is a fixed time delay after the initial spark. This delay is configured to mask the spikes, noise and the like associated with the spark itself. Such delay, however, is conservatively selected to account for variations in the duration of the spark-related noise (e.g., due to the variations in engine speed and load). However, in many instances, this results in a delay in commencing processing, thus effectively ignoring useful information. Additionally, conventional systems do not extend processing of the ion current to the greatest extent possible, also losing information.
Another problem with conventional systems pertains to the unavailability of up-to-date timing information. For example, a known system of the type that uses a main dwell signal (i.e., that defines coil charge initiation and spark timing) uses a so-called current flag as feedback for dwell control. Such current flag is generated when the primary current in the ignition coil reaches a predetermined level. This feedback is used because the main dwell signal can become stale (i.e., available only every two revolutions of the crankshaft in a four cycle IC engine). However, such conventional current flag signals are not used in controlling multicharge operation or in providing overall timing.
In addition, conventional ignition systems are plagued with a proliferation of control, data, and timing lines to the main control unit. It would be desirable to reduce such connections to improve reliability and/or reduce cost.
There is therefore a need to provide an apparatus for detecting a combustion condition or knock condition that minimizes or eliminates one or more of the shortcomings as set forth above.
One object of an ignition apparatus of the present invention is to provide a solution to one or more of the above-identified problems. In general, the invention is characterized by several advantages. One advantage is that it integrates relatively easily into existing ignition systems. Another advantage is that it incorporates closed loop multicharge ignition which provides a longer effective xe2x80x9cspark bumxe2x80x9d time (when appropriate) without interfering with ion sense processing (i.e., determination of both combustion and knock). Still another advantage is that is optimizes a so-called combustion detection window, providing a better base of information upon which to determine a combustion condition including knock. Still yet another advantage is that it minimizes the number of wires required to connect to an existing ignition system (i.e., to a control unit such as an engine control unit). The invention is embodied in several different aspects.
In one aspect of the invention, a current flag trip signal (hereinafter xe2x80x9cCF_Tripxe2x80x9d or CF TRIP signal) is provided for improving (i) closed loop dwell control, (ii) the closing of the combustion window, and (iii) coordinating output signal timing. According to this aspect of the invention, a method is provided for operating a plurality of ignition coils in a multi-cylinder internal combustion engine. The method includes four basic steps. The first step involves initiating combustion in a first cylinder using a first one of the ignition coils. Next, detecting an ionization level in the first cylinder during a combustion window. The third step involves generating a current flag trip signal when a primary current through a second one of the ignition coils meets predetermined criteria. Finally, closing the combustion window for the first cylinder as a function of when the current flag trip signal is generated for the second cylinder. In a preferred embodiment, the second cylinder is the next cylinder in the firing order.
In a second aspect of the invention, the opening of the above combustion window is improved upon by more accurately determining the end of the spark event. According to this aspect of the invention, a method is provided for operating an ignition coil for an internal combustion engine. This method also includes four basic steps. The first step involves generating a spark in a cylinder using the ignition coil wherein a secondary current is established through the ignition coil. Next, determining when the secondary current has discharged to a preselected level and thereafter initiating a delay. The third step involves opening a combustion window after expiration of the delay. Finally, detecting a level of ionization in the subject cylinder during the combustion window.
In third aspect of the invention, a combustion signal indicative of the level of combustion is multiplexed on the same line as the above-mentioned CF_Trip signal, thereby reducing the number of lines or connections in the system (i.e., between the ignition coils and a control unit). In a preferred embodiment, the combustion signal is a pulse width modulation (PWM) signal.
In a fourth aspect of the invention, a knock signal indicative of the level of knock is multiplexed on the same line as a knock window signal (preferably generated by a control unit). This aspect of the invention also reduces the number of lines or connections. In a preferred embodiment, the knock signal is a PWM signal.
In a fifth aspect of the invention, the above-mentioned combustion signal is used to terminate a multicharge mode of operation (i.e., the process of delivering multiple sparks per combustion event per cylinder) so as to not interfere with knock detection. This aspect allows a longer effective xe2x80x9cburn timexe2x80x9d while ensuring knock detection availability.
Other objects, features, and advantages of the present invention will become apparent to one skilled in the art from the following detailed description and accompanying drawings illustrating features of this invention by way of example, but not by way of limitation.